Conventionally, metal-bonded ceramic substrates, in which a metal such as copper (Cu) and aluminum (Al) is bonded to a substrate made from ceramic materials such as alumina (Al2O3), aluminium nitride (AlN), silicon carbide (SiC) and silicon nitride (Si3N4) have been widely used as components of semiconductor devices.
As a method for bonding a metal plate to a ceramic substrate, a direct bonding copper (DBC) method, in which—after a metal plate made from a metal such as copper is placed on a ceramic substrate—the copper plate is directly bonded to the substrate by heating the copper plate at a temperature which is lower than the melting point temperature (1083° C.) of copper and higher than the eutectic point temperature (1065° C.) of copper and oxygen, has been developed and commercially used. Recently, in order to maintain increase of heat emission and a mechanically strong bonding property, ceramic circuit substrates manufactured by an active metal method, in which metal-bonded circuit substrates are bonded through lead layers, have been developed and used in power semiconductors which demand high reliability.
Recently, metal-bonded ceramic substrates have been manufactured by a method of forming the desired circuit patterns by chemically etching a metal plate after the metal plate is bonded to a big ceramic substrate. This method can simultaneously manufacture many circuit substrates, and the manufactured circuit substrate is finally divided into individual substrates by a laser process using carbon dioxide.
The metal-bonded ceramic substrate manufactured by the above method is usually cut and separated into individual circuit substrates, and then a semiconductor-mounting process is performed. In order to increase productivity and work efficiency of the semiconductor-mounting process, a complex arranged substrate manufactured by a laser, not an individual substrate, has been developed. However, since such a complex arranged metal-bonded ceramic substrate is bigger than an individual circuit substrate, it tends to become warped due to its big size. Therefore, in an automation process for mass production, it is difficult to transfer the complex arranged metal-bonded ceramic substrate and fix it in a vacuum environment, and it is liable to be broken when loaded or delivered. Therefore, in order to resolve these problems, various researches for reducing warpage of the complex arranged metal-bonded ceramic substrate have taken place.